1. Field of the Invention
The present invention relates to an optical device having an optical fiber array having one or more optical fibers, and more particularly to an optical device suitable for monitoring signal light while it is being propagated through an optical fiber.
2. Description of the Related Art
With the recent development of wavelength multiplex communications using fiber amplifiers, it has become customary to monitor the amounts of light at respective wavelengths with photodiodes (PD), adjust the amounts of light, and then amplify them with amplifiers.
There are known various methods of monitoring the amounts of light at respective wavelengths. Since the optical fibers need to be coupled to respective monitoring devices, the monitoring devices alone result in a considerable size.
Therefore, there has been a demand for smaller and high density monitoring devices. For monitoring signal light, it is customary for the monitoring device to extract a portion of the signal light. It is desirable for monitoring devices to be able to monitor signal light without largely attenuating the signal light.
Heretofore, a technology disclosed in Japanese Laid-Open Patent Publication No. 2001-264594, for example, has been proposed in the art. According to the disclosed technology, an optical fiber is placed in a V-shaped groove defined in a glass substrate, and thereafter a parallel groove is formed in the glass substrate obliquely to (the optical axis of) the optical fiber. Then, a light reflecting base (optical member) is inserted into the parallel groove, with the gap filled with an ultraviolet-curable resin (adhesive).
Of signal light that is propagated through the optical fiber, a light component (reflected light) that is reflected by the light reflecting base is extracted out of the cladding of the optical fiber. The signal light can be monitored by detecting the reflected light with a photodetector, for example.
If PDs are disposed on optical fibers, then since most of the optical fibers used are single-core optical fibers, PDs in metal packages are often employed (see, for example, Japanese Laid-Open Patent Publication No. 10-300936, Japanese Laid-Open Patent Publication No. 11-133255, and the pamphlet of International Publication No. 97/06458). This is because the single-core optical fibers pose less space limitations and many PDs in metal packages are available on the market and have proven satisfactory as to cost and reliability.
However, it is difficult to use PDs in metal packages in combination with multiple-core optical fibers. In particular, if optical fibers are required to be installed at a high density, e.g., at a pitch of 250 μm, then it is necessary to employ a photodiode array (PD array) comprising a plurality of bare photodiodes.
For the purpose of outputting electrode signals from a PD array, the PD array may be mounted on a wiring board (submount), and the submount may be mounted on a multiple-core optical fiber array.
However, of reflected light from a certain channel, light that passes off the active layer of the PD array or passes through the active layer is reflected by the PD array or the mounting surface of the submount (the surface on which the PD array is mounted), and enters as stray light into another channel, tending to cause crosstalk.
Such crosstalk occurs because the PD array and/or the mounting surface of the submount has an electrode pattern made of a material having a high reflectance or a mounting solder layer.
The above problem arises particularly if the reflected light is applied obliquely to the PD array. Specifically, if the reflected light is applied perpendicularly to the PD array, then since the reflected light is applied perpendicularly to the active layer of the PD array, the reflected light recombines with the same channel (desired channel), causing no crosstalk problem. However, if the reflected light is applied obliquely to the PD array, then since the reflected light hits a material having a high reflectance, it becomes stray light which tends to give rise to problems of crosstalk.